Our primary server had issues at our hosting provider and had to be restored from backup. Posts made after 5/20/2018 11:59PM CDT (UTC -5) and before 5/22/2018 3:00pm CDT may be missing and are not expected to return.

I made my first Dungeon Fantasy Barbarian under the Boxed Set rules.
After buying Tough Skin 3, I noticed the Hurting Yourself rules on the Exploits booklet (p.40) don't exclude this kind of Damage Resistance when striking DR 3+ armor.
The Tough Skin description on the Adventurers booklet (p.16) doesn't talk about it, either.
I searched the Boxed Set PDFs, just in case the Tough Skin exception from B379 was hidden somewhere else, but I couldn't find it.
I know many subtle tweaks have been made to improve Dungeon Fantasy and make it more accessible to new players, so I'm not sure if this is intentional or an overlook.

No. As far as I can tell, in DF Boxed Set there's no difference between rigid and flexible armor.
Since there is no mention of both kinds of armor, I assume the lack of blunt trauma rules is intentional.
That's ok; one of the Boxed Set's design goals was making a simple, standalone game easy to play for newcomers. (And it does a pretty good job at it.)
However, since the rule for hitting DR 3+ from B379 does exist in the Boxed Set, but there is no exception for Tough Skin (which also exists in this ruleset), I'm not sure if it's a design choice or a mistake.